Aug 25 (Reuters) - Canadian oil and gas producer Encana Corp said on Tuesday it will sell its Haynesville natural gas assets in northern Louisiana for $850 million to GEP Haynesville LLC.

Encana also said it will reduce its gathering and midstream investments by about $480 million on an undiscounted basis by 2020.

Under Chief Executive Doug Suttles, Encana has been focusing on transforming into a major oil producer by concentrating spending on regions rich in high-value gas liquids and oil and selling off natural gas assets.

The company has said it plans to invest in oil-rich shale fields of Permian, Eagle Ford, Duvernay and Montney in 2015.